There's been a couple of thread on this, but I haven't seen a simple yes/no answer to this:
If my character channels positive, and I take alignment channel (Evil), can I harm evil outsiders with positive energy?
This is an odd one by Rules as Written.
If you choose "evil", you can harm evil outsiders. You can also heal evil outsiders. Good, neutral, lawful, and chaotic outsiders cannot be healed or harmed by your channeling if you only chose "evil".
Channeling positive or negative energy doesn't matter for Alignment Channel - at least, that is how it is written.
For PFS games, it follows Rules as Written strictly. For my own house rule games, we usually try to make alignment channel polarized like it's interaction with "positive / negative" energy beings. In other words, per my house rule, if someone chooses to harm evil outsiders, they can only harm evil outsiders and only heal good outsiders. If someone chooses to only harm lawful outsiders, they can only heal chaotic outsiders. Still, that is just a house rule.
